1. Technical Field
The invention relates generally to integrated circuit (IC) fabrication, and more particularly, to an electrically programmable diffusion resistor and methods of forming the same.
2. Background Art
Conventional bipolar complementary metal oxide semiconductor (BiCMOS) integrated circuits often require resistors with very high precision. For example, existing BiCMOS technologies generally offer resistors with 15-20% tolerance. Resistor tolerances down to approximately 10% are also available in BiCMOS technologies, but require increased cost and process complexity.
One approach to provide high precision resistors (for example, in III-V (gallium arsenic (GaAs), indium phosphorous (InP), etc) technologies) uses a laser to remove materials from the resistor, thus increasing the resistance value. The trimming continues with the integrated circuit being tested until the required resistance is obtained. Tolerances down to 0.1% may be achieved using this approach. Unfortunately, this method is extremely costly and impractical for a volume production BiCMOS technology.
In another approach, electrically programmable fuses are implemented that can be used to selectively eliminate portions of resistor banks to achieve tighter resistor tolerances. This approach does not require additional masking steps, but requires a large area due to the size of the resistor bank structures, as well as the associated circuitry and pads required for programming. This increased size adds cost by increasing required chip area. In addition, there are parasitic effects associated with the large resistor banks. Finally, only finite adjustments can be made using the fuse trimming technique.